JP2005277036A - Manufacturing method of flexible printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a flexible printed circuit board small in dimension change rate which does not cause a change in dimension in forming a circuit by removing the unnecessary part of a metallic conductor by etching. <P>SOLUTION: This manufacturing method of the flexible printed circuit board made of a conductor layer and a polyimide layer includes steps of directly applying a polyimide precursor resin solution on a conductor, drying, and curing by thermal treatment. The method is characterized in that a ratio of making the polyimide precursor resin layer into imide is controlled to a range of 12-18%, before the curing process carried out after drying at 150°C or lower and carried out at a drying temperature or higher. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a flexible printed circuit board, and more particularly to a method for manufacturing a flexible printed circuit board by directly applying a polyimide resin onto a conductor.

  Conventionally, a flexible printed circuit board is manufactured by bonding a polyimide film on a conductor using an adhesive such as an epoxy resin or a urethane resin. The polyimide film itself has excellent heat resistance, but the heat resistance of the adhesive is inferior, causing problems such as blistering and peeling when heated to a high temperature with solder, or reducing the flame resistance of the circuit. It was. In addition, there is a problem that the dimensions change when heated to a high temperature, and the adhesive is affected by various chemicals used when processing into a circuit, resulting in a decrease in adhesive strength.

  On the other hand, as a method of manufacturing a flexible printed circuit board by directly applying a polyimide precursor resin solution onto a conductor such as copper foil, curling caused by the difference in the thermal expansion coefficient between the conductor and the resin after being applied and cured. A method for correcting (for example, see Patent Document 1) and a method for preventing curling by applying a low thermal expansion resin (for example, see Patent Document 2) have been proposed, but none of them is sufficient. Therefore, a method of preventing curling by drying a certain amount of solvent at a certain temperature range before proceeding with the curing reaction (see, for example, Patent Document 3) has been proposed.

However, since this method did not consider the imidation ratio of the intermediate product after drying, it was subsequently cured by heat treatment, and the resulting flexible printed circuit board was etched to remove unnecessary portions of the metal conductor, thereby forming a circuit. The problem of dimensional change (hereinafter referred to as dimensional change rate) occurred. Moreover, although there is a report on the imidization ratio and curl of the intermediate product after drying (see, for example, Patent Document 4), it is not practical because of its wide range.
JP-A-56-23791 JP-A-60-243120 Japanese Patent Laid-Open No. 1-245587 Japanese Patent Laid-Open No. 5-13902

  In view of the above-described problems of the prior art, the present invention eliminates unnecessary portions of metal conductors by etching a flexible printed circuit board and does not cause a dimensional change (hereinafter referred to as a dimensional change rate) when forming a circuit. An object is to obtain a flexible printed circuit board with a small change rate.

  As a result of various studies in order to solve the above problems, the present inventors have controlled the imidation ratio of the intermediate product before the curing step after coating and drying within a specific range, thereby reducing the dimensional change rate. The present invention was completed by finding that a printed circuit board can be obtained.

  That is, the present invention is a method for producing a flexible printed board comprising a conductor layer and a polyimide layer by applying and drying a polyimide precursor resin solution directly on a conductor and then drying it at 150 ° C. or less. Then, the imidation rate in the polyimide precursor resin layer before the curing step performed at a temperature equal to or higher than the drying temperature is controlled to be in a range of 12 to 18%.

As a preferred embodiment of the present invention, at least two types of polyimide precursor resin solutions that are directly applied onto a conductor are coated on a plurality of layers, dried a plurality of times, and an imidation ratio before curing is 12 It is desirable to set it to ˜18% and finally harden it by heat treatment at the end.
Moreover, as a preferable aspect of the present invention, it is desirable that the first layer and the second layer are applied and dried, and the third layer is applied thereon and dried, followed by heat treatment.

（但し、式中Ｒ₁〜Ｒ₈は水素、ハロゲン、低級アルコキシ基、低級アルキル基のいずれかであり、そのうちの少なくとも１つは低級アルコキシ基である）で示される構成単位を有するポリアミドイミド前駆体樹脂であることが望ましい。 Furthermore, as a preferable aspect of the present invention, at least one of the polyimide precursor resins is represented by the following general formula (1).

(Wherein R _{1 to} R ₈ are any one of hydrogen, halogen, a lower alkoxy group, and a lower alkyl group, at least one of which is a lower alkoxy group). A body resin is desirable.

  ADVANTAGE OF THE INVENTION According to this invention, the flexible printed circuit board excellent in workability | operativity with a small dimensional change rate can be easily manufactured, except the unnecessary part of the metal conductor after an etching.

  In the present invention, the polyimide precursor resin includes a polyimide precursor resin, a polyamide imide precursor resin, and a polyimide ester precursor, which do not substantially contain a closed imide ring in the molecule and generate an imide bond by heat curing. Body resin and the like, typically polyamic acid. A polyimide precursor resin obtained by reacting a diamine containing diaminobenzanilide or a derivative thereof with an aromatic tetracarboxylic anhydride is preferable.

（但し、式中Ｒ₁〜Ｒ₈は水素、ハロゲン、低級アルコキシ基、低級アルキル基のいずれかであり、そのうちの少なくとも１つは低級アルコキシ基である）で示される構成単位を有するポリアミドイミド前駆体樹脂である。 Particularly preferably, at least one of the polyimide precursor resins is represented by the following general formula (1)

(Wherein R _{1 to} R ₈ are any one of hydrogen, halogen, a lower alkoxy group, and a lower alkyl group, at least one of which is a lower alkoxy group). Body resin.

（但し、式中Ｒ₁〜Ｒ₈は上記の場合と同じである）で示されるジアミノベンズアニリド誘導体とを反応させて得られる。 The polyamide precursor resin of the general formula (1) is composed of pyromellitic anhydride which is an aromatic tetracarboxylic anhydride and the following general formula (2).

It is obtained by reacting with a diaminobenzanilide derivative represented by the formula (wherein R _{1 to} R ₈ are the same as those described above).

で示される２’−メトキシ−４，４’−ジアミノベンズアニリドである。 Here, the diaminobenzanilide derivative needs to have at least one lower alkoxy group as a substituent. The term “lower” here means 10 or less carbon atoms, and if the carbon number exceeds 10, the heat resistance is lowered, which is not preferable. The lower alkoxy group is preferably a methoxy group or an ethoxy group, and more preferably an alkoxy group is present at the ortho position of the amide bond from the viewpoint of improving water absorption. More preferably, from the point of being cheap, the formula (3)

2′-methoxy-4,4′-diaminobenzanilide represented by the formula:

  The synthesis reaction of such a polyimide precursor resin is generally performed by N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc) amide solvent, dimethyl sulfoxide (DMSO), The reaction is carried out in a solvent such as dimethyl sulfate, sulfolane, butyrolactone, cresol, phenol, halogenated phenol, cyclohexanone, dioxane, tetrahydrofuran, diglyme and the like at a reaction temperature of 0 to 200 ° C, preferably 0 to 100 ° C. By mixing approximately equimolar amounts of the diamine compound and the acid anhydride compound that react with the above general formula in these solvents, a precursor solution of the polyimide resin can be obtained.

In the present invention, such a polyimide-based precursor resin solution is directly applied onto a conductor, but any method can be used as an application method, for example, a barcode method, a gravure coating method, a roll coating method, Examples include a die coating method. The die coating method is preferable because bubbles are not involved in the resin solution. In the present invention, it is desirable to apply at least two kinds of polyimide precursor resin solutions to be applied directly on the conductor so as to form a plurality of layers, and the imidization ratio after drying a plurality of times is 12 to 18 %, And finally hardened by heat treatment. Here, the imidization ratio is a percentage of the absorbance of the imide group when the resin layer sample after drying is obtained by measuring the absorbance of the absorption wavelength of 1780 cm ⁻¹ of the imide group by infrared absorption analysis, and 100% imidization of the sample. It is the value calculated as.

  Drying is performed at 150 ° C. or lower, preferably 130 ° C. or lower, and the imidization ratio at this stage is controlled to 12 to 18%, preferably 14 to 16%. When drying is strong and the imidization rate exceeds 18%, the dimensional change rate of the flexible printed circuit board shifts to the shrink side, and when drying is weak and the imidization rate is less than 12%, the dimensional change rate tends to shift to the expansion side. Show. In any case, the unnecessary portion of copper is removed by etching, and the dimensional change rate when forming a circuit is large, which is not practical. Moreover, it is preferable that the intermediate | middle goods after drying whose imidation rate is 12 to 18% are 30 weight% or more with respect to the polyimide obtained by making it harden | cure after that.

  Curing as used herein refers to a step of forcibly promoting imidization reaction to promote resin curing. This imidization reaction usually proceeds rapidly at a temperature exceeding 150 ° C., particularly at a temperature exceeding 160 ° C. Thus, after evaporating a certain amount or more of the solvent, curing is performed at a temperature exceeding 150 ° C. In order to sufficiently perform the imidization reaction, the maximum curing temperature is 250 ° C or more, preferably 300 ° C or more. is there. In this curing step, if the temperature is rapidly increased, foaming of the resin may occur. Therefore, it is preferable to perform a multistage heat treatment or a continuous temperature raising heat treatment.

  Although any process can be adopted as such a drying step and a curing step, it is preferable to use a floating type in which the applied conductor does not contact the apparatus. In the floating type, the conductor is dried and cured in a state where it is suspended in the airflow, and the airflow is uniformly generated from nozzles arranged above or below the conductor surface while the conductor is continuously running. The conductor is blown out toward the conductor surface, and the running conductor is floated, and it is made to travel while curving so as to hit a wave.

  Heating is preferably performed by blowing hot air as an air stream, but infrared heating, electromagnetic induction heating, or the like may be used or used in combination. As the heating atmosphere, any of air, an inert gas such as nitrogen, carbon gas, and argon can be selected.

  Examples of the conductor used for the flexible printed circuit board according to the present invention include copper, aluminum, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, and alloys thereof. Copper is preferred. In addition, for the purpose of improving the adhesive strength of the conductor, chemicals such as siding, nickel plating, copper-zinc alloy plating, or aluminum alcoholate, aluminum chelate, silane coupling agent, anchor coating with good adhesive resin, etc. A mechanical surface treatment may be applied.

  Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is of course not limited thereto.

The residual solvent ratio in each example was determined by weight reduction when the intermediate polyimide precursor after coating and drying was heated at 170 ° C. for 60 minutes. The imidation rate was determined by obtaining the absorbance at an absorption wavelength of 1780 cm ⁻¹ of the imide group by infrared absorption analysis, and taking the percentage of the absorbance of the imide group when the sample was imidized 100%. The dimensional change rate was obtained from the dimensional change rate before and after copper etching. The dimensional change rate of + means curling to the conductor side, and-means curling to the side opposite to the conductor side.

In addition, the symbol in each example is as follows.
PMDA: pyromellitic dianhydride BTDA: 3,3′-4,4′-benzophenone tetracarboxylic dianhydride DDE: 4,4′-diaminodiphenyl ether MABA: 2′-methoxy-4,4′-diaminobenz Anilide BAPP: 2,2′-bis [4- (4-aminophenoxy) phenyl] propane DMAC: dimethylacetamide

Synthesis example 1
After 6 mol of BAPP was dissolved in 44 kg of DMAC, it was cooled to 10 ° C., 6 mol of BTDA was gradually added and reacted to obtain a viscous polyimide precursor resin (polyamic acid A).

Synthesis example 2
After 32 mol of MABA and 8 mol of DDE were dissolved in 124 kg of DMAC, the mixture was cooled to 10 ° C., 40 mol of PMDA was gradually added and reacted to obtain a viscous polyimide precursor resin (polyamic acid B).

Example 1
The copper foil was coated such that the first layer was polyamic acid A, the second layer was polyamic acid B, the third layer was polyamic acid A, and the respective film thicknesses were 3, 20, and 3 μm. The second layer was dried in a floating drying oven at 100 ° C. for 2 minutes. Thereafter, the third layer was applied and dried by running in a drying furnace at 135 ° C. at a line speed of 3 m / min for about 5 minutes. The residual solvent ratio of the intermediate product at this time was 15%. Next, curing was carried out by running a plurality of floating type curing furnaces whose temperatures were sequentially increased from 130 to 360 ° C., thereby obtaining a copper-clad article having a resin layer thickness of 25 μm. The obtained copper-clad product, that is, the flexible printed circuit board, had a good dimensional change rate of 0%.

Example 2
In the drying process after coating the third layer, the line speed was made faster than that in Example 1 to obtain an intermediate product having an imidization rate of 12%. Other than this, a flexible printed circuit board was prepared in the same manner as in Example 1 above. The obtained flexible printed circuit board had a dimensional change rate of + 0.03%.

Example 3
In the drying process after application of the third layer, the line speed was set slightly higher than in Example 1 to obtain an intermediate product having an imidization ratio of 14%. Other than this, a flexible printed circuit board was prepared in the same manner as in Example 1 above. The obtained flexible printed circuit board had a dimensional change rate of + 0.01%.

Example 4
In the drying process after application of the third layer, the line speed was slightly slower than in Example 1 to obtain an intermediate product having an imidization ratio of 16%. Other than this, a flexible printed circuit board was prepared in the same manner as in Example 1 above. The obtained flexible printed circuit board had a dimensional change rate of -0.01%.

Example 5
In the drying process after application of the third layer, the line speed was made slower than in Example 1 to obtain an intermediate product having an imidization ratio of 18%. Other than this, a flexible printed circuit board was prepared in the same manner as in Example 1 above. The obtained flexible printed circuit board had a dimensional change rate of -0.03%.

Comparative Example 1
In the drying process after application of the third layer, the line speed was made faster than in Example 1 to obtain an intermediate product having an imidization rate of 9%. Other than this, a flexible printed circuit board was prepared in the same manner as in Example 1 above. The obtained flexible printed circuit board had a dimensional change rate of + 0.06%.

Comparative Example 2
In the drying process after application of the third layer, the line speed was made slower than in Example 1 to obtain an intermediate product having an imidization rate of 25%. Other than this, a flexible printed circuit board was prepared in the same manner as in Example 1 above. The obtained flexible printed circuit board had a dimensional change rate of -0.06%.

Claims (4)

  In the method of manufacturing a flexible printed circuit board composed of a conductor layer and a polyimide layer by directly applying and drying a polyimide precursor resin solution on a conductor and then drying it, after drying at 150 ° C. or lower, The manufacturing method of the flexible printed circuit board which controls the imidation ratio in the polyimide precursor resin layer before the hardening process performed at temperature in the range of 12 to 18%.   At least two or more types of polyimide precursor resin solutions to be applied directly on the conductor, each of which is applied to a plurality of layers, dried a plurality of times, and the imidization ratio before the curing step is set to 12 to 18%. The method for producing a flexible printed circuit board according to claim 1, wherein the flexible printed circuit board is cured by heat treatment.   The manufacturing method of the flexible printed circuit board of Claim 2 which heat-processes, after apply | coating and drying a 1st layer and a 2nd layer, apply | coating and drying a 3rd layer on it. At least one of the polyimide precursor resins is represented by the following general formula (1)

(Wherein R _{1 to} R ₈ are any one of hydrogen, halogen, a lower alkoxy group, and a lower alkyl group, at least one of which is a lower alkoxy group). It is a body resin, The manufacturing method of the flexible printed circuit board of any one of Claims 1-3.